Which of the following substances are present on the rubbing surface of a…

Safety matches ignite through friction: the match head carries an oxidiser and fuel, while the separate striking surface on the box carries an abrasive plus a mild source of phosphorus. Because elemental white phosphorus is dangerously reactive, toxic, and ignites spontaneously in air, safety-match manufacture uses only its stable allotrope, red phosphorus, paired with a coarse abrasive that generates the localized heat needed to trigger ignition.

On a standard matchbox, that abrasive is powdered glass mixed with red phosphorus, coated onto the striking strip. When the match head is drawn across this rough, phosphorus-laced surface, friction generates enough heat to convert a trace of red phosphorus to white phosphorus vapour, which ignites and, in turn, sets off the oxidiser in the match head. This matches the composition glass powder and red phosphorus.

• White phosphorus is pyrophoric and highly toxic (historically linked to 'phossy jaw' among matchworkers), so it is excluded from the striking mixture; only its safe red allotrope is used.

• Magnesium is a flammable metal burned for its brilliant white light in flares and fireworks; it plays no role in generating striking friction and is absent from match compositions.

• Elemental potassium reacts violently with atmospheric moisture and cannot be coated onto a consumer product; combined with unstable white phosphorus, this pairing is doubly unsafe and unused.

Hence, the substances present on the rubbing surface are glass powder and red phosphorus.